community/1-code-suggestions.md

title: Code Suggestions sidebar_position: 1 description: Apache ShenYu Coding Guide author: “xiaoyu” categories: “Apache ShenYu” tags: [“Code Suggestions”] date: 2019-09-22 cover: “/img/architecture/shenyu-framework.png”

General

Use as many lambda function expressions as possible.
Method parameters must be modified with final.
Constants modified static final must be named in upper case.
Methods should not have too many parameters.
Clear unused classes and methods.
Use linux line separators.
Tab size is 4 and keep indents on empty lines.
All code passage of Checkstyle: https://github.com/apache/shenyu/blob/master/script/shenyu_checkstyle.xml
When adding a new file, you need to add the apache protocol in the header of the file.

Object

Use Optional transform Null.

Optional.ofNullable(xxx).orElse(obj)

Use Objects Judgment Null Or NotNull.

Objects.isNull(obj) OR Objects.nonNull(obj)

Use Objects.equals Judgment are they equal.

Objects.equals(obj1, obj2)

Creater objects outside of a for loop.

Object object = null;
for () {
    object = new Object();
}

Collection

must indicate initial capacity to avoid recalculate capacity.

List

Use LinkedList when you need to add or delete elements, Else use ArrayList.
Use org.apache.commons.collections4.CollectionUtils Judgment Is empty Or Not empty.

CollectionUtils.isEmpty(list) or CollectionUtils.isNotEmpty(data)

Map

Use ConcurrenHashMap when considering concurrency of threads, Else use HashMap.
Iterate over map using the most efficient way Or use lambda function.

Set<Map.Entry<String, String>> entrySet = map.entrySet();
Iterator<Map.Entry<String, String>> iter = entrySet.iterator();
while (iter.hasNext()) {
        Map.Entry<String, String> entry = iter.next();
      
}

String

Use org.apache.commons.lang3.StringUtils Judgment Is empty Or Not empty.

StringUtils.isEmpty(list) or StringUtils.isNotEmpty(data)

String.join should be used when string concatenation occurs.

String join(CharSequence delimiter, CharSequence... elements)

Exception

Do not use try...catch in a loop, it should be on the outermost layer.

try {
  for () {
  }
} catch () {
  
}

Do not use printStackTrace().
Please use custom exceptions or ShenyuException.

Resource

Please use try with resource to close resource.

Several methods to judge and handle Null

Judge self if Null or not, and also need to transform self, below are some representative examples:
current : result.setXXX(null == a ? b.getXXX() : b.getXXX(a));
recommendation : Optional.ofNullable(a).map(b::getXXX).orElse(b.getXXX());
current : return null == a ? b.newC() : b.newC(a.getD(), a.getE());
recommendation : return Optional.ofNullable(a).map(e -> b.newC(e.getD(),e.getE())).orElse(b.newC());
current : return null == a.getB() ? null : a.getB().getC();
recommendation : return Optional.ofNullable(a.getB()).map(C::getD).orElse(null);
current : return null == a ? new B() : C.newD(a);
recommendation : return Optional.ofNullable(a).map(B::newC).orElse(new D());
Directly compare current object with Null, below are some representative examples:
current : public void xxx（Object o）{if(null == o){retrun;}}
current : public boolean wasNull() {return null == currentRow;}
recommendation ：Use JDK8's Objects.isNull method.
Judge self if Null or not, and also need to return self related ternary operator, below are some representative examples:
current : this.a = null == a ? new B().newC() : a;
recommendation : Optional.ofNullable(a).orElse(new B().newC());
current : a = null == a ? b.getC().getD() : a;
recommendation : a = Optional.ofNullable(a).orElse(b.getC().getD());
current : return null == a.getB() ? c : a.getB();
recommendation : return Optional.ofNullable(a.getB()).orElse(c);
current :
```
BigDecimal c;
BigDecimal s;
if (null == c) {
  c = new BigDecimal("0");
}
if (null == s) {
  s = new BigDecimal("0");
}
```
recommendation : c = Optional.ofNullable(c).orElse(new BigDecimal("0")); s = Optional.ofNullable(s).orElse(new BigDecimal("0"));
current : return null == results.get(0) ? 0 : results.get(0);
recommendation : return Optional.ofNullable(results.get(0)).orElse(0);
current : return null == getA().getB() ? Collections.emptyList() : Collections.singletonList(getA().getB());
recommendation : return Optional.ofNullable(getA().getB()).map(Collections::singletonList).orElse(Collections.emptyList());
Judge self if Null or not, and also need to return self independent ternary operator, below are some representative examples:
current : A a = null == b ? cMap.values().iterator().next() : cMap.get(d);
current : return null == a ? new B() : new B(c);
recommendation : No modification.
Judge collection is null or not, below are some representative examples:
current :
```
private boolean isEmpty(final List<String> xxx) {
    return null == xxx || xxx.isEmpty();
}
```
recommendation : Add a collection tool class to make unified judgment.

Judge Map's value is Null or not, below are some representative examples:
current :

public Collection<String> getA(final String b) {
   Collection<String> result = cMap.get(b);
   if (null == result) {
      result = Collections.emptySet();
   }
   return result;
}

recommendation : Use Map.getOrDefault() method.

public Collection<String> getA(final String b) {
  return cMap.getOrDefault(b, Collections.emptySet());
}

Judge is Null or not, if yes throw exception, else execute next step, below are some representative examples:
current :

private Collection<String> doXxx(final Collection<String> a, final Object<?> b) {
  if (null == c) {
     throw new Exception("XXX");
  }
  return c.doXxx(a,new Object(b.getXXX(), b.getXXX(), b.getXXX()));
}

recommendation :

private Collection<String> doXxx(final Collection<String> a, final Object<?> b) {
     return Optional.ofNullable(c).map(e -> e.doXxx(a,
            new Object(b.getXXX(), b.getXXX(), b.getXXX())))
           .orElseThrow(()-> new Exception("XXX"));
}

Judge is Null or not, and return Optional wrapped object, below are some representative examples:
current : return null == a ? Optional.empty() : Optional.ofNullable(a.getXXX());
recommendation : return Optional.ofNullable(a).map(e -> e.getXXX());